Angular aperture

About: Angular aperture is a research topic. Over the lifetime, 1771 publications have been published within this topic receiving 27257 citations.

Controlling the contribution of the electric field components to the focus of a high-aperture lens using binary phase structures

Abstract: We show that the contribution of the electric field components into the focal region can be controlled using binary phase structures. We discuss differently polarized incident waves, for each case suggesting easily implemented binary phase distributions that ensure a maximum contribution of a definite electric field component on the optical axis. A decrease in the size of the central focal spot produced by a high numerical aperture (NA) focusing system comes as the result of the spatial redistribution of the contribution of different electric field components into the focal region. Using a polarization conversion matrix of a high NA lens and the numerical simulation of the focusing system in Debye’s approximation, we demonstrate benefits of using asymmetric to polar angle ϕ binary phase distributions (such as arg[cos ϕ] or arg[sin 2ϕ]) for generating a subwavelength focal spot in separate electric field components. Additional binary structure variations with respect to the azimuthal angle also make possible controlling the longitudinal distribution of light. In particular, the contribution of the transverse components in the focal plane can be reduced by the use of a simple axicon-like structure that serves to enhance the NA of the lens central part, redirecting the energy from focal plane. As compared with the superimposition of a narrow annular aperture, this approach is more energy efficient, and as compared with the Toraldo filters, it is easier to control when applied to three-dimensional focal shaping.

Magneto-optical disk system with specified thickness for protective layer relative to the numerical aperture of the objective lens

Abstract: A magneto-optical disc system includes a magneto-optical disc with a light-transmitting cover, an objective lens for bundling or focusing a laser beam on a magnetic recording layer of the magneto-optical disc in order to perform recording and/or reproduction, and a magnetic field generating unit obtained by forming a coil pattern in an optical glass. In the above system, the thickness t 2 of the light-transmitting cover is set to fall within the range of 0.6 to 0.1 mm, and the numerical aperture (NA) of the objective lens is set to fall within the range of 0.55 to 0.70, so as to obtain high-density recording and/or reproduction by permitting the lens to be quite close to the actual recording layer.

Lens module with low chromatic aberration

Abstract: Provided is a lens module for imaging an object on an image plane. In the order from the object side to the image side of the lens module, the lens module includes a first lens made of glass and having positive refraction power, a second lens made of plastic and having negative refraction power, a aperture stopper, a third lens having positive refraction power, and a fourth lens having negative refraction power. The lens module satisfies the following formula: Vd 1 −Vd 2 ≧35; wherein, Vd 1 is the Abbe number of the first lens in d light and Vd 2 is the Abbe number of the second lens in the d light.

Achromatic Combinations of Half-Wave Plates

Abstract: The plane of polarization of two or more wavelengths can be rotated by a predetermined amount through the use of two or more identical half-wave plates in series, the axes of which are oriented at predetermined angles with respect to the incident plane of polarization. For two wavelengths a rotation of 90° may be accomplished by the use of two plates with their slow axes at angles of 22.5°+δ and 67.5°−δ, respectively. For three wavelengths a 90° rotation is obtained by using three plates at angles of 11.25°+δ, 45°, and 78.75°−δ respectively. The quantity δ is a small angle usually less than 1° which determines the spectral range of achromatization. Identical half-wave plates are easily obtained by cutting a single splitting of mica or a plane parallel sheet of other birefringent material. The wavelength for which the plates have half-wave retardation is not critical. Rather than having a smaller angular aperture than the single half-wave plate, the three-element achromatic rotator has a larger angular aperture. The use of the stereographic projection of the Poincare sphere for graphical solution of polarized light problems is discussed briefly.